As someone who plays Garen and Darius, I agree with what the others posted. Darius is a win lane, lose game kind of champion if you don't share kills. A good game for Darius is when he has lots of assists and doesn't ult much. I typically only ult to secure kills and when dueling/know I'll die if I don't. It's much more effective to pull a low health enemy and/or slow them so your carry can clean the kill than it is to ult them.
Garen has insane team fight presence. He can get away with building tanky and still do crazy damage. Spinning through an entire team, taking focus, silencing the biggest threat, and applying Black Cleaver debuffs to the enemy is insanely strong. With a Warmogs and Visage (when appropriate), Garen is almost always full health when a fight breaks out. Throw in an anti-tank nuke, and you have a much stronger champion than Darius. --- Currently playing: games